Verapamil Prophylaxis for Postoperative Atrial Dysrhythmias: A Prospective, Randomized, Double-blind Study Using Drug Level Monitoring

Orally administered verapamil hydrochloride (80 mg every 8 hours) or a placebo was given to 109 patients after coronary artery bypass grafting in a randomized, double-blind manner to test the efficacy of verapamil in preventing postoperative atrial dysrhythmias. The test drug was given through a nasogastric tube beginning 4 to 6 hours after operation until oral ingestion was possible. Serum levels of verapamil were measured at selected times after operation and when postoperative atrial dysrhythmias occurred. Postoperative atrial dysrhythmias occurred in 10 of the 53 verapamil-treated patients and in 20 of the 56 placebo-treated patients. Patients with verapamil drug levels higher than 150 ng/ml had fewer postoperative atrial dysrhythmias than those with lesser verapamil levels (p = .034) or than placebo-treated patients (p = .012). Only 2 of 31 patients with drug levels higher than 150 ng/ml experienced postoperative atrial dysrhythmias. Approximately 40% of verapamil-treated patients had drug levels lower than 150 ng/ml at 48 hours after operation. It is concluded that oral administration of verapamil prevents postoperative atrial dysrhythmias in a dose-dependent fashion.